Hunting and fishing remain essential activities for humanity's recreation in the developed world and our survival in some parts of the developing world. Since before recorded history, humans has been mimicking objects to attract, pacify, repel, or otherwise elicit desired behaviors in animals. These objects have been used as lures, decoys, camouflage, scare devices, coverings, traps and other uses where visually deceiving or otherwise visually convincing an animal was necessary to elicit a desired response.
Human color definition is also an ancient practice that continues to be refined. Isaac Newton famously labeled ROY-G-BIV (red, orange, yellow, green, blue, indigo and violet) when viewing light through a prism. Sensitivity versus wavelength curves of human vision were derived before modern analytical techniques proved that the underlying physical mechanism was light absorption of photoreceptors. These sensitivity curves and experimental research led to the development of accurate human color coordinate systems such as those based around the L,a,b color space (a color-opponent space with dimension “L” for lightness and viable “a” and “b” for the color-opponent dimension) and RGB (Red-Green-Blue) color spaces. It is understood that humans have three types of wavelength discriminating photoreceptors called cones in their retinas which, along with neural circuitry, define the three primary colors RGB from which all human perceived colors can be created by mixing light of these primary colors.
The body of knowledge about animal vision has been growing through observational experiments, and more recently through spectroscopic and genetic techniques. While the number of species examined is small, we now know that birds, fish, mammals, and invertebrates have a variety of color vision systems. Individual species with color vision typically fall into three categories: dichromatic (two types of photoreceptor cones), trichromatic (three types of cones), or tetrachromatic (four types of cones). The spectral sensitivity curves of cone photoreceptors also vary considerably between species. Additional specializations have also been identified. The number of cones and their respective spectral sensitivity curves are significant factors in the perception of color in humans and animals. A cone's spectral sensitivity curve defines which wavelengths produce a neural response and how strongly that response is.
The visual spectrum of animals and human can be likened to a radio dial spectrum. The visual spectrum of humans can be seen by looking at a rainbow or light split in a prism. The spectrum has a beginning and an end similar to how the FM radio dial spectrum goes from 88 megahertz to 108 megahertz. In humans the visual spectrum is generally accepted to run from 400 nanometers (deepest blue/violet) to 700 nanometers (deepest red). Each animal species has its own spectrum with many species perceiving light as low as 320 nanometers for example. The cones can be likened to broad-band radio receivers that “listen” for signals across a wide swath of the spectrum, hearing all stations in their listening band as an aggregated mixed signal and outputting a neural signal relating to the overall loudness of all of the stations in the band. Continuing the radio analogy, some stations on parts of the band are perceived as louder than others of the same radio broadcasting strength because the cone is more sensitive to the center of its band and less sensitive toward the edges of the band (defined by the spectral sensitivity curve). In reality, the band is a wide swath of the animal's perceivable rainbow (visual spectrum) and the determination of aggregate “loudness” (or neural signal strength) of the band is achieved by the combined neural signal of many proximal (nearby) cones of the same type on the retina.
A retina contains the photoreceptors of an eye in a repeating mosaic pattern and is analogous to an image sensor array on a digital camera. Continuing with the analogy, a small grouping of photoreceptors making up the repeating unit in the mosaic pattern can be thought of, for illustrative purposes, as defining a pixel (all of the pixels together define the image). What color that retinal “pixel” is perceived to be, by the brain of the animal or human, is determined by the signal coming from the neural circuitry that is part of the pixel consisting of nerve cells surrounding the photoreceptors. The perceived pixel color is determined by the ratio of the effective signal strengths of the different types of cones on each pixel.
Continuing the pixel analogy, a dichromatic animal, with two types of cones, perceives color of the retinal “pixel” based on the signal strength ratio of just two cone signal channels (because a dichromatic animal only has two types of cones, each with a spectral sensitivity curve covering a wide swath of the visual spectrum). A trichromatic animal (including humans) perceives the color of a pixel based on the ratio of three cone signal channels. A tetrachromatic animal has four cone channels. It's important to note that just because, for example, two species might both be trichromatic, they do not necessarily perceive the same colors for the same “pixel” areas of an image. The cone's spectral sensitivity curve defines the signal strength that affects the ratio of cone signals coming from a “pixel” which determines the color perceived. For two species to perceive the same color from the same pixel area of an image, the number of types of cones, each cone's spectral sensitivity curve, and the visual neural circuitry must be the same. This may occur in species with no genetic difference in the part of their respective DNA which defines the morphology of their visions system. But narrow adaptation is often the norm and even species so close in DNA that interbreeding is possible can have diverging spectral sensitivity curves of their respective cones.
The light spectra that stimulate cones in a retina results in signal channels from each cone type to the brain which perceives the color. That light spectra's photons striking the cone came from a source, such as the sun. The sun, like any light source, has an emission spectra. The emission spectra strike an object, such as a leaf. The leaf absorbs some of the spectra and the rest is reflected and some of the reflected light strikes the eye of the observer. The amount of the spectra that is absorbed is different across the spectra (each wavelength has specific reflection). For the example of the leaf, some areas of the visual spectrum, such as what humans would call blues or reds, are significantly absorbed and the part of the visual spectrum humans perceive as green is absorbed less. The resultant reflectance spectra leaving the leaf's surface is now changed from the sun's incident spectra that hit the leaf. The leaf's reflectance spectra travels to the observer and passes through the ocular media in the observer's eye and finally a portion of the photons of the spectra strike the photoreceptor cells. The ocular media includes the cornea, the aqueous humor, the lens and the vitreous humor. These structures of the ocular media are generally transparent but have areas of the visual spectrum where some absorbance occurs. In fact, the cut-off edge, especially on the shorter wavelength side, of the visual spectrum is often defined by the ocular media. The structures of the ocular media each act as filters, absorbing parts of the incident spectra.
Critical to the present invention is the fact that color “metamers” are two or more light spectra which are not identical yet are perceived as identical colors by an observer. Human metamers are exploited in every color matching technology utilized for paints, plastics, fabrics, film and electronic displays.
A metamer is unique to the observer species. Animal species with differing cone photoreceptor types and specialized sensitivity curves have their own unique metamers. This has been understood by visual neuroscientists and correctly pointed out by Johnson et al in US Patent Application No. 2007/0200337 which teaches avoidance of human metamers by spectral matching when attempting to visually deceive animals. In terms of color matching, the opposite of a metamer match is a spectral match. By matching the spectral reflectance curve of the target object to be mimicked, Johnson teaches that the mimic will appear identical in perceived color to every observer species, regardless of cone photoreceptor type or sensitivity curves. A “spectral match”, as taught by Johnson et al, would then enable the mimic to be used for multiple species and no knowledge of the animal's vision system is needed.
“Source metamerism” is the phenomenon where a metamer match is only a metamer match for a particular spectra of incident light shining on a reflecting object. This is most noticeable to humans when two color matched objects are suddenly noticeably different colors when the light source is changed, such as from sunlight to indoor fluorescent lighting.
Numerous patents and applications exist regarding specific colors which purport to elicit specific responses in target animals including the use of human-invisible “colors” such as those in ultraviolet (UV) wavelengths. Yutaka et al in the abstract of JP2002238403 teaches UV reflection in fishing lures, Halliday in U.S. Pat. No. 7,189,128 teaches blue and UV reflection which purport to elicit specific behaviors in fish, and Johnson in US Pat. Application No. 2007/0200337 teaches spectral curve matching to mimic objects including in the ultraviolet wavelengths. Numerous military camouflage patents teach spectral matching of infrared (IR) signatures to avoid detection by IR imagers. Hunting camouflage patents such as Neitz et al in U.S. Pat. No. 5,409,760 teaches coloration which exploits the neutral point of ungulates' (hoofed animals') vision.
Pigments, dyes and other colorants have been extensively classified for their effect on human color coordinates, including their effect when mixed with binders and other colorants. Colorants have cost, performance, toxicity, compatibility and other tradeoffs irrespective of their particular color, which must be taken into account when formulating colored objects. Unfortunately, nature's “colors” such as those found on fur, skin, scales, feathers, bark, leaves and other natural objects are often “colored” with bio-pigments such as carotenoids, chlorophyll, and melanins which are not always hydro-stable, thermo-stable or UV stable, nor are they always compatible with ink and paint solvents and as such can make very poor pigments for man-made coatings. Nature also seldom provides minerals or otherwise coating-friendly pigments or colorants which match the reflectance spectra of the surfaces of living things. Because of this fact, spectral matching is very difficult, expensive, and even (for some spectra) unachievable as a viable man-made coating or colorant system that will last in the field or be affordable. Without spectral curve matching, current man-made objects designed to be observed by animals contain human metamers and as such often look significantly different in color to the target animal. This incorrect animal “color match” can reduce the effectiveness of the object's intended function. What is needed is a method to produce a color match to a target animal without the disadvantages of spectral curve matching.
No accurate models of animal vision systems exist which approach the accuracy of human color coordinate systems. Because of the likelihood that a color which is “matched” to human eyes (a human metamer) will not be a metamer to an animal, the only current approach to successfully mimicking a surface appearance in the eyes of a target animal is through spectral matching as taught by Johnson et al. But given the severe limitations of spectral matching, what is needed is an alternative approach to creating a successful mimic.
No viable methods exist to create animal metamers. Such a method and the compositions created from said method would enable successful mimicry of surfaces without the difficulty and disadvantages of spectral matching. While Johnson et al. teaches the opposite of metamer matching (via spectral matching), the present invention teaches a method of metamer matching to create animal metamers.
What is needed is a method to successfully mimic the appearance of a target object in the visual system of a target animal which is affordable, practical, and achievable. What is needed is a method which creates animal metamers and which can also evaluate how a particular composition would be perceived by multiple species including humans to select the best trade-off composition for a given application. What are needed are technically and commercially viable compositions which impart surface appearances which are metamers of the surface appearances of target objects in the visual system of target animals.